Marianne Maertens

• Group Leader at Technische Universität Berlin

Human performance in psychophysical detection and discrimination tasks is limited by inner noise. It is unclear to what extent this inner noise arises from early noise (e.g., in the photoreceptors) or from late noise (at or immediately prior to the decision stage, presumably in cortex). Very likely, the behaviorally limiting inner noise is a nontri...

One well-established characteristic of early visual processing is the contrast sensitivity function (CSF) which describes how sensitivity varies with the spatial frequency (SF) content of the visual input. The CSF prompted the development of a now standard model of spatial vision. It represents the visual input by activity in orientation- and SF se...

A key question in perception research is how stimulus variations translate into perceptual magnitudes, that is, the perceptual encoding process. As experimenters, we cannot probe perceptual magnitudes directly, but infer the encoding process from responses obtained in a psychophysical experiment. The most prominent experimental technique to measure...

The apparent brightness of a target region is determined not only by its local luminance, but also by its surrounding context. This is well demonstrated by the many illusions where some surround context causes two physically identical targets to appear different in brightness (e.g. White's (1979) illusion). Here we use perceptual scales from Maximu...

How does the human visual system extract relevant information from the pattern of light on the retinae? The psychophysical study of early vision has led to important insights in the initial processing characteristics of human vision, and we have image-computable models which quantitatively account for relevant psychophysical findings. Many of these...

Visual stimuli are at the heart of perception research. They may come as visual illusions which demonstrate the striking differences between the perceptual and physical world, they may involve minuscule stimulus changes which are used to probe the limits of visual sensitivity, or they may be used to probe any other aspect of visual processing. stim...

Find poster here: http://dx.doi.org/10.13140/RG.2.2.11382.06726

Human vision relies on mechanisms that respond to luminance edges in space and time. Most edge models use orientation-selective mechanisms on multiple spatial scales and operate on static inputs assuming that edge processing occurs within a single fixational instance. Recent studies, however, demonstrate functionally relevant temporal modulations o...

Human vision relies on mechanisms that respond to luminance edges in space and time. Most edge models use orientation-selective mechanisms on multiple spatial scales and operate on static inputs assuming that edge processing occurs within a single fixational instance. Recent studies, however, demonstrate functionally relevant temporal modulations o...

Luminance discontinuities, i.e. edges, are important visual image features because they demarcate the boundaries of objects in the physical world. Psychophysically, human edge sensitivity has been studied in different ways including edge localization, edge polarity judgments, near-threshold edge detection or reverse correlation techniques. Differen...

White’s effect is an example of how the brightness of an image region depends both on its local luminance and on its surround. The effect is commonly measured using a matching task, where observers adjust the luminance of a test patch so as to match the brightness of a target. However, a perceptual match might not always be possible, as the context...

One fundamental question in vision research is how the retinal input is segmented into perceptually relevant variables. A striking example of this segmentation process is transparency perception, in which luminance information in one location contributes to two perceptual variables: the properties of the transparent medium itself and of what is bei...

Various image-computable models have been proposed to describe the relationship between local luminance, visual context, and perceived luminance (brightness) or perceived reflectance (lightness). Classically, these models are tested on a subset of relevant stimuli. While specific failure cases have been shown for most models, a systematic overview...

Computational models are a useful tool to characterize the mechanisms underlying visual perception. They avoid the ambiguity inherent in verbal model descriptions, and, when published together with the code, they can be (re-)used by different people and their predictions can be replicated in a straight-forward way. For this reason, many journals no...

Multiscale spatial filtering models account for a variety of phenomena in human lightness perception, such as Simultaneous Contrast and White's illusion, by combining outputs of oriented filters at multiple scales. However, it was shown that these models were unable to account for spatial frequency specific effects of narrowband noise on White's il...

In psychophysics (without access to physiological measurements at retina and the behaviourally relevant stages within the visual system), early and late noise in within the visual system seem hard to tell apart because discrimination depends on the inner noise or effective noise which is a non-trivial combination of early and late noises. In this w...

A central question in psychophysical research is how perceptual differences between stimuli translate into physical differences and vice versa. Characterizing such a psychophysical scale would reveal how a stimulus is converted into a perceptual event, particularly under changes in viewing conditions (e.g., illumination). Various methods exist to d...

One central problem in perception research is to understand how internal experiences are linked to physical variables. Most commonly, this relationship is measured using the method of adjustment, but this has two shortcomings: The perceptual scales that relate physical and perceptual variables are not measured directly, and the method often require...

Maximum likelihood difference scaling (MLDS) is a method for the estimation of perceptual scales based on the judgment of differences in stimulus appearance (Maloney & Yang, 2003). MLDS has recently also been used to estimate near-threshold discrimination performance (Devinck & Knoblauch, 2012). Using MLDS as a psychophysical method for sensitivity...

Perceived lightness is often measured by asking observers to specify a test field that best matches their percept of a target. Typically one is interested in measuring lightness constancy, i.e. to what extent observers choose the same matches across viewing contexts that lead to variations in the luminance signal of the target. Such a procedure is...

It is still an unresolved question how the visual system perceives surface lightness given the ambiguity of the sensory input signal. We studied lightness perception using two-dimensional images of variegated checkerboards shown as perspective projections of three-dimensional objects. We manipulated the contrast of a target check relative to its su...

We investigate human viewing behavior when participants are presented with physical realizations of 3D objects by gathering fixations on the surface of the presented stimuli. This data is used to validate assumptions regarding visual saliency so far only experimentally analyzed using flat stimuli. We provide a way to compare fixation sequences from...

Spatial filtering models are currently a widely accepted mechanistic account of human lightness perception. Their popularity can be ascribed to two reasons: They correctly predict how human observers perceive a variety of lightness illusions, and the processing steps involved in the models bear an apparent resemblance with known physiological mecha...

We recently showed that a contrast-based model of lightness perception outperformed a number of other models in predicting lightness matches across different viewing conditions (Zeiner & Maertens, 2014; Maertens & Shapley, 2013). By considering regional variations in contrast range, the model successfully predicted lightness constancy across change...

Human observers perceive the lightness of surfaces accurately despite substantial variations in illumination and viewing conditions. It is known that the lightness of an image region is influenced by its surroundings, but the exact mechanism for this contextual modulation is not yet understood. We recently proposed a contrast-based lightness model...

Maximum likelihood difference scaling (MLDS) is a method for the estimation of perceptual scales based on an equal-variance, Gaussian, signal detection model (Maloney & Yang, 2003). It has recently been shown that perceptual scales derived with MLDS allowed the prediction of near-threshold discrimination performance for the Watercolor effect (Devin...

White's illusion is the perceptual effect that two equiluminant gray patches superimposed on a black-and-white square-wave grating appear different in lightness: A test patch placed on a dark stripe of the grating looks lighter than one placed on a light stripe. Although the effect does not depend on the aspect ratio of the test patches, and thus o...

We investigate the premise that robust grasping performance is enabled by exploiting constraints present in the environment. These constraints, leveraged through motion in contact, counteract uncertainty in state variables relevant to grasp success. Given this premise, grasping becomes a process of successive exploitation of environmental constrain...

IN THE PRESENT EXPERIMENT WE ADDRESSED THE QUESTION OF HOW THE VISUAL SYSTEM DETERMINES SURFACE LIGHTNESS FROM LUMINANCES IN THE RETINAL IMAGE WE MEASURED THE PERCEIVED LIGHTNESS OF TARGET SURFACES THAT WERE EMBEDDED IN CUSTOM-MADE CHECKERBOARDS THE CHECKERBOARDS CONSISTED OF 10 BY 10 CHECKS OF 10 DIFFERENT REFLECTANCE VALUES THAT WERE ARRANGED RAN...

Visual perception of object attributes such as surface lightness is crucial for successful interaction with the environment. How the visual system assigns lightness to image regions is not yet understood. It has been shown that the context in which a surface is embedded influences its perceived lightness, but whether that influence involves predomi...

The color of achromatic surfaces, i.e. their perceived reflectance, can only indirectly be inferred from the luminance image in the retina. Variations in illumination as well as different 'atmospheres' such as transparent media located between the object and our eyes may dramatically alter the luminance of one and the same object. Adelson (2000) pr...

The present paper deals with the classical question how a psychological experience, in this case apparent lightness, is linked by intervening neural processing to physical variables. We address two methodological issues: (a) how does one know the appropriate physical variable (what is the right x?) to look at, and (b) how can behavioral measurement...

A fundamental question in visual perception research is whether the sensitivity to stimulus differences is limited by the sensory representation of the external stimulus, that is, the proximal stimulus, or by its perceptual representation, i.e., stimulus appearance. In the domain of lightness perception, the question translates into whether discrim...

Background / Purpose: We investigated whether dihedral angles between surfaces viewed as 2D projections on a screen are perceived veridically. Main conclusion: We found that dihedral angle perception is biased towards 90 degrees.

The grouping of image parts into a perceptual whole can help to deduce an objects' shape when it is only partially visible. Here we studied the temporal characteristics of the process of grouping parts into wholes by measuring eye movements during visual search. Visual search for an occlusion-defined surface among non-surface stimuli can proceed ef...

When we asked observers to perform a discrimination task with stimuli that were either geometrically organized in order to produce a subjective shape or disorganized in order to provide only local stimulus information, observers casually reported that the organized stimulus appeared to persist longer than the misaligned one. Therefore in the curren...

Objects in our visual environment are arranged in depth and hence there is a considerable amount of overlap and occlusion in the image they generate on the retina. In order to properly segment the image into figure and background, boundary interpolation is required even across large distances. Here we study the cortical mechanisms involved in colli...

There is a distinct visual process that triggers the perception of illusory surfaces and contours along the intersections of aligned, zigzag line patterns. Such illusory contours and surfaces are qualitatively different from illusory contours of the Kanizsa type. The illusory contours and surfaces in this case are not the product of occlusion and d...

Objects in our visual environment are perceived as integral wholes even when their retinal images are incomplete. We ask whether the perceptual precision of subjective interpolation between isolated image parts depends on the overall proportion of visible image information or rather on its geometrical arrangement. We used Varin-type subjective shap...

Our visual percepts are not fully determined by the physical stimulus input. That is why we perceive crisp bounding contours even in the absence of luminance-defined borders in visual illusions such as the Kanizsa figure. It is important to understand which neural processes are involved in creating these artificial visual experiences because this m...

Event-related functional magnetic resonance imaging signal change in Heschl's gyrus and the planum temporale was found to reflect sensory decisions about target presence. In a dichotic listening task, activation was higher for target present responses, irrespective of actual target presence. In fact, activation was highest for false alarms, that is...

In an event-related fMRI study, we investigated the neural correlates of visual dimension and response changes. We used a compound task, which required target selection by a singleton feature, a unique color or motion direction, before the appropriate motor response, which was determined by target orientation, could be selected. Both types of chang...

With practice, we become increasingly efficient at visual object comparisons. This may be due to the formation of a memory template that not only binds individual features together to create an object, but also links the object with an associated response. In a longitudinal fMRI study of object matching, evidence for this link between perception an...

Perceptual learning involves the specific and relatively permanent modification of perception following a sensory experience. In psychophysical experiments, the specificity of the learning effects to the trained stimulus attributes (e.g., visual field position or stimulus orientation) is often attributed to assumed neural modifications at an early...

Visual matches are sometimes faster when stimuli are presented across visual hemifields, compared to within-field matching. Using a cued geometric figure matching task, we investigated the influence of computational complexity vs. processing efficiency on this bilateral distribution advantage (BDA). Computational complexity was manipulated by requi...

Patients with lesions of the splenium showed higher validity effects of visuospatial cues than did patients with partial lesions of the corpus callosum anterior to the splenium and control participants. Many of the patients tested had also shown a left-ear suppression for consonant-vowel syllables in a previous dichotic listening study. The authors...

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The authors found splenial lesions to be associated with left ear suppression in dichotic listening of consonant-vowel syllables. This was found in both a rapid presentation dichotic monitoring task and a standard dichotic listening task, ruling out attentional limitations in the processing of high stimulus loads as a confounding factor. Moreover,...

Zugl.: Leipzig, Univ., Diss., 2006